Cryogenic refrigerator

ABSTRACT

A Stirling-cycle refrigerator within a straight cylindrical housing, with a drive means inbetween aligned compression and displacer pistons which are axially movable to define variablevolume compression and expansion spaces, heat exchangers at opposite ends of the housing adjacent the pistons respectively, a regenerator carried by the displacer, and a gas duct interconnecting the variable-volume spaces.

I wnltfid States Patent 1 1 1 1 3,736,761

Richmond et al. 1 1 June 5, 1973 54 CRYOGENIC REFRIGERATOR 3,220,201 11/1965 Henchling ..60/24 3,323,314 6/1967 Dros .....62 6 Inventory Thomas Rlchmond, Cumberland; 3,552,120 1 1971 Beale ..62i6

Peter K. Bertsch, Esmond, both of R.l. Primary ExaminerWilliam J. Wye [73] Assignee: U.S. Philips Corporation, New Att0mey Fra"k Tnfan York, NY.

57 ABSTRACT 22 Filed: Aug. 9, 1971 1 [21] Appl. No.: 170,316 A Stirling-cycle refrigerator within a straight cylindrical housing, with a drive means inbetween aligned compression and displacer pistons which are axially 52 U.S. c1 ..62/6, 60/24 movable to define variablewolume Compression and [51] Int. Cl ..F25b 9/00 expansion spaces heat exchangers at opposite ends of Fleld of Search the housing adjacent pistons respectively a regenerator carried by the displacer, and a gas duct in- [56] References Cited terconneeting the variable-volume spaces.

UNITED STATES PATENTS 11 Claims, 10 Drawing Figures 3,147,600 9/1964 Maloker ..62/6

PAIENTEUJUN 5 I973 Fig. 3

SHEET 2 OF 4 Fig.4

SHEET 3 [IF 4 CRYOGENIC REFRIGERATOR BACKGROUND OF THE INVENTION Cryogenic refrigerators operating on the Stirlingcycle principal have been made with a variety of standard configurations, all of which provide variable volume compression and expansion spaces at relatively higher and lower temperatures, a regenerator inbetween the two spaces, and means such as out-of-phase pistons for reversibly compressing, transporting, and expanding the gas in stages through the compression space, the regenerator, and the expansion space.

One of the basic configurations includes a compression piston and a displacer piston arrange in-line with co-linear piston rods both of which are driven by a single crank mechanism, and between the pistons is a fixed arrangement of cooler, regenerator, and freezer elements. In an alternate configuration a single crank drives a compression piston and expansion displacer at approximately right angles in separate cylinders and between the remote ends of the expansion and compression spaces are the freezer, a cooler and regenerator, all interconnected by a gas duct. A variation of this latter design is a parallel arrangement of cylinders for the compression and displacer pistons with the variable volume compression and expansion spaces being defined in the remote portions of the two cylinders and connected with a gas duct which also includes the freezer regenerator and cooler. In certain cases the compression piston and displacer have been arranged in-line but in opposed relationship with the cooler regenerator and freezer fixedly disposed in the space between them; then the two movable pistons are driven by separate drive means. A further variation in cryogenic refrigerator construction involves the incorporation of the displacer piston and the regenerator into a unitary component both of which move together each time this component is oscillated out of phase in relation to the compression piston. In this last configuration the manner of driving the compression piston and displacer is typically to extend the displacer connection rod coaxially with the compression displacer rod such that both rods engage a crank mechanism of a single motor.

In all these devices in which refrigeration has been achieved to various degrees of success, the structures are substantially bulky due to the scattered arrangement of dual cylinders or the dual crank-shaft drive mechanism for two separate pistons. In one of the most important uses of these cryogenic refrigerators, namely to cool components in infrared detection systems, it is essential that the devices be operable over a long time period without need for repair, adjustment or replacement of parts. Accordingly the working parts should be highly reliable in all aspects of their operation; however, it has been found repeatedly that the components which fail either partially or totally, are generally elements of the drive mechanism such as the various cranks, bearings and connection arms.

Two other common problems are internal vibration due to dynamic imbalance generally inherent in these apparatus, external imbalance where the entire housing of non-symmetrical components is rotated for example, and excess weight resulting from efforts to achieve a well-balanced system.

The prior art is furthermore characterized in that the compression piston and the displacer have axial move ment defining an out-of-phase relationship. Under certain circumstances it might be desired or necessary to change the phase difference, which could be achieved only by dismantling the mechanism and substituting a different crank or related components for effecting the stroke and period of motion. Finally there is consideration of the warm heat exchanger component of these refrigerators; typically this heat exchanger is formed by external cooling fins extending outward from the compression chamber, with the fins typically occupying considerable and excessive space. In numerous military and general scientific uses of these refrigerators, less than perfect operation and reliability is intolerable, and renders such apparatus essentially useless. In attempts to overcome these problems and achieve the reliability called for, manufacture of these devices has become quite expensive due to better quality materials and more complex mechanism; and to some extent the de sired reliability and/or small size has not been available at any cost. The new invention described below has successfully overcome the various disadvantages and imperfections of the prior art with a very compact and highly reliable device.

SUMMARY OF THE INVENTION The present invention comprises a Stirling cycle refrigerator having a variable volume compression space and a cold finger defining a variable volume expansion space operable at a lower temperature than the compression space. The compression space and cold finger are at opposite ends of an elongated closed housing, with a warm heat exchanger at the distal part of the compression space and a cold heat exchanger at the distal part of the cold finger. Adjacent the warm heat exchanger is a compression piston axially movable in the housing for defining the variable volume compression space; and adjacent the cold heat exchanger is a displacer piston with a regenerator extending therefrom toward the cold heat exchanger. The compression and displacer pistons are engaged by a single electric motor disposed between them with coupling means for driving the two pistons in a predetermined phase relationship. Finally there is a gas passage interconnecting the warm heat exchanger and the portion of the expansion space remote from the cold heat exchanger. In this configuration the pistons and the regenerator and heat exchangers are all aligned generally linearly in a single straight cylindrical housing.

In the preferred embodiment of this invention the coupling means between each output drive shaft of the electric motor and the corresponding piston is formed by a beveled pinion gear secured axially to the motor shaft and a mating beveled gear rotatable about an axis normal to that of the pinion. On the surface of the beveled gear is an eccentric pin which operates as a crank for driving the respective piston via a connecting rod. The coupling for the displacer piston is generally similar to that of the compression piston and is disposed at the opposite end of the electric motor, such that the various components of this refrigerator are all coaligned within a single straight cylindrical housing. Such an arrangement is extremely compact and generally of smaller overall dimensions than any comparable cryogenic refrigerator. The drive mechanism and coupling means are particularly reliable as compared with prior art mechanisms, because the various components are both simple and very few in number. A four-to-one changer fins along the length of the outside refrigerator casing for heat exchange with air or other fluid flowing adjacent these fins; alternatively, the fins may be helical, so that rotation of the housing in still air, for example, will drive the air axially along the length of the housing. The cooling means can also be provided by clamping a heat sink to the smooth cylindrical outside diameter of the new refrigerator. The present invention will now be described in greater detail with reference to the drawings showing the preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation view of the preferred embodiment.

. FIG. 2 is an end view of FIG. 1.

FIG. 3 is an elevation view in section, of the refrigerator in FIG. 1.

FIG. 4 is a top plan view in section of the refrigerator in FIG. 1.

FIG. 5 is an exploded view in perspective of the FIG. 1 embodiment.

FIG. 6 is a top plan view of a second embodiment of the invention.

FIG. 7 is a top plan view in section, of the apparatus in FIG. 6.

FIG. 8 is a front elevation view in section of the apparatus in FIG. 6.

FIGS. 9 and 10 are diagrammatic view of two Stirling cycle refrigerators.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first preferred embodiment is shown in FIGS. 1-5 and the second embodiment in FIGS. 6-8. The refrigerator 10 in FIG. 1 has a cylindrical housing 11 with a cold finger 12 at one end and a valve 13 through which the apparatus is charged with a quality of working medium such as helium gas.

The internal components of this embodiment are shown diagrammatically in FIG. 3 and 4, wherein the housing 11 of the refrigerator 10 has an electric motor 14 mounted centrally, with two opposite output shafts and a pinion bevel gear l5, 16 on each shaft. Cooperating with pinion 16 is a driven bevel gear 17 which is rotatable about its central axis l8l8, but has an eccentric crank pin 19 that oscillates the piston rod 20 and compression piston 21 linearly within compression cylinder 22. At the motors opposite end pinion l5 simultaneously drives bevel gear 23 about its axis 23a with an eccentric crank pin 24 similar to pin 19, engaged to piston rod assembly 25 which oscillates via rod 25 the displacer-regenerator 26 within the cold finger 12. In this embodiment the displacer 26 is the double expansion type with a larger-diameter part 26a having a first regenerator therein, and a small-diameter part 26b with a second regenerator. The cylindrical housing of this cold finger 12 cooperates with the stepped displacer to define first and second expansion spaces 27 and 28, and the cold-end heat exchanger or freezer 29.

The helium compressed in compression space 21a by piston 21 is communicated via duct 30 along longitudinal ducts 31 and 32, to the space 33 adjacent the rear end of the displacer 26a. Seals 34-39 contain the helium from leaking along the path of these ducts, which ducts perform the further function of being the warm heat exchanger component of the Stirling cycle refrigerators thermodynamic system. The outer surface of housing 1 1, may define the effective heat exchange surface, or fins may be extended outward from this surface along the length of the housing, as exemplified by straight fin segment 40 or helical fin segment 41 in FIG. 5. Where air or other cooling medium flows adjacent these fins, the straight configuration 40 is generally suitable; where the cooling medium is relatively stationary, but the refrigerator is rotated, the helix configuration 41 will induce the medium to flow generally axially and produce the same heat exchange effect.

With the compact arrangement of components shown, the refrigerator comprises an elongated cylinder with a center longitudinal axis about which the assembly is readily balancable and thus rotatable, even at high speeds. The operation of this refrigerator as regards it thermodynamic cycle is similar to typical prior art Stirling cycle refrigerators, with the usual components: compressor 21, 22 cooler, 30, 31, 32 regenerator 26, expansion means 27 (second regenerator and expansion means 26b, 28) and freezer 29. The phase difference of the compressor piston and the displacer is variable merely by re-setting the rotative position of the bevel gear 23 relative to bevel gear 17, which can be done by adjusting the hub position of pinion 15 or 16.

FIG. 5 shows in detail substantially all of the parts for the assembly of FIGS. 1-4, with the same reference numerals on corresponding parts such as housing 11, motor 14, pinions l5, l6, bevel gears 17, 23, compression piston 21, displacer-regenerator 26, charging valve 13, etc.. One feature of the invention that is shown most clearly in FIG. 5 is the grooves 42 in sleeve 43 which fits within housing 11 and encompasses the motor and associated mechanism. The space between each groove 42 and the outer housing 11 defines a longitudinal duct through which the helium or other working medium is communicated from the compression space within cylinder 22 to the expansion space within the cold finger. The gas duct as thus described is a convenient and efficient means for transporting the gas, and for using the gas duct as its own extended heat exchange member. l

The second embodiment of the invention shown in FIGS. 6-8, is substantially similar to the first embodiment, except for the following differences: Thecold finger 50 has only one expansion space 51 in which the single-diameter, displacer-regenerator 52 is axially movable; and the charging valve 53 is located at the hot or compression end of the housing. FIG. 8 shows more clearly than before, an internal duct 54 through which compressed gas from the compressor is communicated to the expansion space 55 in the cold finger 50, and also an electrical connector 58 leading to the motor 59. For this second embodiment, suggested sizes for the major components are as follows: the bevel gear-andpinion has a 4:1 ratio; the motor has six poles and operates at 7,200 rpm; the compression piston 60 has 25/32 inch diameter with 0.322 stroke or 1 inch diameter with 0.322 stroke; and the connecting rods 61 have a typical 6:1 l/r ratio where l is rod length and r is bevel gear crank radius. The two bevel gears and corresponding piston 60 and displacer 52 are 90 out-of-phase, which is of course, variable.

According to the present invention, and as shown diagrammatically in FIG. 9, the compression space 60a communicates to the cold finger 61 in which the displacer 62 has a regenerator 63 incorporated therein, thus providing a moving regenerator. Alternatively, as shown in FIG. 10, the regenerator 64 could be fixed in place within the cold finger 65, with gas from the compressor 66 passing via duct 69 first through this fixed regenerator 64 and then to the expansion space 67 as driven by the displacer 68.

What is claimed is:

1. A Stirling-cycle refrigerator having a variable volume compression space, and a cold finger defining a variable volume expansion space operable at a lower average temperature than that of the compression space, comprising: an elongated, closed housing having in one end said compression space and at the opposite end the cold finger, a warm heat exchanger at the distal part of the compression space, a compression piston axially movable in the compression space adjacent and inward of the warm heat exchanger, said cold finger comprising a cylindrical part, a cold heat exchanger at the distal end thereof, a displacer piston axially movable in the cylinder part, thus defining said variable volume expansion space with a far end adjacent the cold heat exchanger and an opposite near end, and a regenerator carried by the displacer adjacent the cold heat exchanger, drive means intermediate and engaged to the compression and displacer pistons to oscillate the pistons with a pre-selected phase difference, the drive means being a single motor with dual drive shafts extending from opposite ends, and coupling means between each of said shafts and the compression and displacer pistons respectively, and a gas duct interconnecting the warm heat exchanger and the near end of the expansion space.

2. Apparatus according to claim 1 wherein the coupling means at each motor shaft comprises a bevelled pinion gear secured axially to the shaft, a mating bevel gear rotatable about an axis normal to said shaft, an eccentric pin carried by the bevel gear and operable as a crank, and a connecting rod secured between the pin and the corresponding piston for oscillating same axially.

3. Apparatus according to claim 2 wherein at least one of said couplings means is adjustable to vary the angle of said phase difference between the two pistons.

4. A Stirling-cycle refrigerator having a variable volume compression space, and a cold finger defining a variable volume expansion space operable at a lower average temperature than that of the compression space, comprising: an elongated, closed housing having in one end said compression space, and at the opposite end the cold finger, a warm heat exchanger at the distal part of the compression space, a compression piston axially movable in the compression space adjacent and inward of the warm heat exchanger, said cold finger comprising a cylindrical part with a regenerator for receiving gas from the warm heat exchanger, a cold heat exchanger adjacent the regenerator for expansion of gas from said regenerator, and a displacer piston spaced from the compression piston and axially movable to provide said variable volume space for gas in the cold finger, drive means between the compression and displacer pistons and engaged to said pistons to oscillate them with a pre-selected phase difference, the drive means being a single motor with dual drive shafts extending from opposite ends, and coupling means between each of said shafts and the compression and displacer pistons respectively, and gas duct means interconnecting the warm heat exchanger and the expansion space.

5. Apparatus according to claim 4 wherein the regenerator is disposed at the remote end opposite the warm heat exchanger, and the cold heat exchanger is disposed intermediate the regenerator and the cold piston.

6. Apparatus according to claim 5 wherein said regenerator is fixed in place.

7. A Stirling-cycle refrigerator having a variable volume compression space, a cold finger defining a variable volume expansion space operable at a lower aver age temperature than that of the compression space, and a warm heat exchanger, and further comprising: an elongated, closed housing having in one end said compression space and at the opposite end said cold finger, the housing wall defining an outer surface operable as the .warm heat exchanger and a compression piston axially movable in the compression space, said cold finger comprising a cylindrical part, a cold heat exchanger at the distal end of the cold finger, a displacer piston axially movable in the cylinder part, thus defining said variable volume expansion space, and a regenerator carried by the displacer, drive means intermediate and engaged to the compression and displacer pistons to oscillate the pistons with a pre-selected phase difference, the drive means being a single motor with dual drive shafts extending from opposite ends, and coupling means between each of said shafts and the compression and displacer pistons respectively, and a gas duct interconnecting the warn heat exchanger and the expansion space, this duct extending along the length of and in heat exchange relationship with the inside surface of the housing wall which is thermally conductive to said outer surface thereof.

8. Apparatus according to claim 7 further comprising cooling fins extending outward from the outer surface of said housing.

9. Apparatus according to claim 8 wherein said fins extend generally radially outward and longitudinally along the length of the housing.

10. Apparatus according to claim 8 wherein the fins extend outward from the outer surface of the housing, and wind around the housing defining a curve such as a spiral or helix.

11. Apparatus according to claim 8 wherein said cooling fins are separate elements from the housing, are disposed and secured in intimate physical contact with the housing for good thermal conductivity.

# i t i i 

1. A Stirling-cycle refrigerator having a variable volume compression space, and a cold finger defining a variable volume expansion space operable at a lower average temperature than that of the compression space, comprising: an elongated, closed housing having in one end said compression space and at the opposite end the cold finger, a warm heat exchanger at the distal part of the compression space, a compression piston axially movable in the compression space adjacent and inward of the warm heat exchanger, said cold finger comprising a cylindrical part, a cold heat exchanger at the distal end thEreof, a displacer piston axially movable in the cylinder part, thus defining said variable volume expansion space with a far end adjacent the cold heat exchanger and an opposite near end, and a regenerator carried by the displacer adjacent the cold heat exchanger, drive means intermediate and engaged to the compression and displacer pistons to oscillate the pistons with a pre-selected phase difference, the drive means being a single motor with dual drive shafts extending from opposite ends, and coupling means between each of said shafts and the compression and displacer pistons respectively, and a gas duct interconnecting the warm heat exchanger and the near end of the expansion space.
 2. Apparatus according to claim 1 wherein the coupling means at each motor shaft comprises a bevelled pinion gear secured axially to the shaft, a mating bevel gear rotatable about an axis normal to said shaft, an eccentric pin carried by the bevel gear and operable as a crank, and a connecting rod secured between the pin and the corresponding piston for oscillating same axially.
 3. Apparatus according to claim 2 wherein at least one of said couplings means is adjustable to vary the angle of said phase difference between the two pistons.
 4. A Stirling-cycle refrigerator having a variable volume compression space, and a cold finger defining a variable volume expansion space operable at a lower average temperature than that of the compression space, comprising: an elongated, closed housing having in one end said compression space, and at the opposite end the cold finger, a warm heat exchanger at the distal part of the compression space, a compression piston axially movable in the compression space adjacent and inward of the warm heat exchanger, said cold finger comprising a cylindrical part with a regenerator for receiving gas from the warm heat exchanger, a cold heat exchanger adjacent the regenerator for expansion of gas from said regenerator, and a displacer piston spaced from the compression piston and axially movable to provide said variable volume space for gas in the cold finger, drive means between the compression and displacer pistons and engaged to said pistons to oscillate them with a pre-selected phase difference, the drive means being a single motor with dual drive shafts extending from opposite ends, and coupling means between each of said shafts and the compression and displacer pistons respectively, and gas duct means interconnecting the warm heat exchanger and the expansion space.
 5. Apparatus according to claim 4 wherein the regenerator is disposed at the remote end opposite the warm heat exchanger, and the cold heat exchanger is disposed intermediate the regenerator and the cold piston.
 6. Apparatus according to claim 5 wherein said regenerator is fixed in place.
 7. A Stirling-cycle refrigerator having a variable volume compression space, a cold finger defining a variable volume expansion space operable at a lower average temperature than that of the compression space, and a warm heat exchanger, and further comprising: an elongated, closed housing having in one end said compression space and at the opposite end said cold finger, the housing wall defining an outer surface operable as the warm heat exchanger and a compression piston axially movable in the compression space, said cold finger comprising a cylindrical part, a cold heat exchanger at the distal end of the cold finger, a displacer piston axially movable in the cylinder part, thus defining said variable volume expansion space, and a regenerator carried by the displacer, drive means intermediate and engaged to the compression and displacer pistons to oscillate the pistons with a pre-selected phase difference, the drive means being a single motor with dual drive shafts extending from opposite ends, and coupling means between each of said shafts and the compression and displacer pistons respectively, and a gas duct interconnecting the warn heat exchanger and the expansion space, this duct extending along the length of and in heat exchange relationship with the inside surface of the housing wall which is thermally conductive to said outer surface thereof.
 8. Apparatus according to claim 7 further comprising cooling fins extending outward from the outer surface of said housing.
 9. Apparatus according to claim 8 wherein said fins extend generally radially outward and longitudinally along the length of the housing.
 10. Apparatus according to claim 8 wherein the fins extend outward from the outer surface of the housing, and wind around the housing defining a curve such as a spiral or helix.
 11. Apparatus according to claim 8 wherein said cooling fins are separate elements from the housing, are disposed and secured in intimate physical contact with the housing for good thermal conductivity. 